part of internal;

class State {
   Position head;
   int start;

   State () {
      head = new Position(0, 0);
      start = 0;
   }
}

class Position {
   int line;
   int char;

   Position (this.line, this.char) {
      if (line == null) throw null_arg;
      if (char == null) throw null_arg;
   }

   bool get isValid {
      if (line < 0) return false;
      if (char < 0) return false;
      return true;
   }
}
